Wait so... how do I actually PLAY as the new characters?

[Something Hank]

It literally does not matter what character I pick in the Character Select room. If I then step into All Zones Mode, any individual zone, daily challenge, etc... it then just puts me into another room of "choose your next character" and I only get 9 options. In fact, the others aren't even 'locked', they're just not there.

Iihh... I don't REMEMBER it working this way but now I can't even access my OLD DLC anymore. What's going on? Did I break something?

EDIT: Yeah I'm... I'm just fully confused now. Go into Character Select, pick Nocturna. Back in the lobby. Pick Zone 5.

Then I'm forced to repick a character from the base 9 characters. I simply am not allowed to play as any of the DLC characters now and I'm... I'm so confused.

[temp]

You might want to check your custom rules cuz it sounds like you're playing in the "All Characters" mode.
Go to Customize > Custom Rules > Gameplay Options > Extra Modes and set the Multi-Character setting to None, or go to the Presets tab and load Default Rules if you don't intend to have custom rules at all.